The invention relates to improvements in writing implements in general, and more particularly to writing improvements in implements which can be used with advantage in numerically controlled and other automatic drafting or like machines. Still more particularly, the invention relates to improvements in writing implements of the type wherein the width of lines to be drawn on the surface of a sheet of paper or another suitable information carrier is determined by the width of the front end face of the tip of the implement and wherein the implement is provided with means for supplying a flowable medium (such as ink or India ink) to the front end face of the tip.
It is already known to provide a writing implement, particularly a drawing pen, with a tubular tip whose front end face comes in contact with the surface which is to be provided with a line. Such implements can draw lines of reasonably satisfactory quality and are often employed in numerically controlled automatic drafting machines, e.g., in those known as plotters. A drawback of implements with tips in the form of tubes which must directly engage the surface of the information carrier is that the tubes must be made of a high-quality material which can stand extensive wear. This is especially important if the lines are to be drawn on rough surfaces, such as the surfaces of unpolished or non-calendered carriers. The useful life of tubular tips is relatively short, even when the tips are made of high-quality material, if the machine is to draw lines on relatively rough surfaces. The majority of presently known tubular tips are disposable, but it is already known to provide such tips with inserts of hard metal. This contributes significantly to the initial cost of the writing implements without appreciably prolonging the useful lives of the tips when the implements are used to draw lines of rough surfaces. In such instances, even a tip with an expensive insert of hard metal must be dispensed with after a relatively short period of use.
It is further known to provide the tip of a writing implement with a ball which rolls along the surface of an information carrier and deposits thereon a layer of ink or another flowable material to thus form a line having a width depending on the width of the area of contact between the ball and the surface. The construction of these writing implements (popularly known as ball point pens) is such that nearly one-half of the ball projects from the tip of the implement, i.e., the difference between the dimensions of the confined and exposed portions of the ball should barely suffice to ensure that the ball is reliably retained in its socket. The ball deposits on the surface of a carrier a flowable medium which is normally of pasty consistency, and the width of the line depends upon the force with which the exposed portion of the ball is urged against and deforms the material of the carrier.
It was further proposed to design a ball point pen in such a way that the ball is mounted for forward and rearward movement in the tip of the housing of the implement and is biased forwardly by a spring. Such implements, also called and/or used as marking pens, are disclosed, for example, in German Auslegeschrift No. 1 209 912 of Schwarzaugl, in U.S. Pat. No. 1,563,408 to Sutherland, in German Offenlegungsschrift No. 25 59 158 of Chaumet and in French Pat. No. 950.038 to Roussel. The purpose of the springs which bias the ball is to ensure that the pressure with which the implement is urged toward the writing or drafting surface cannot unduly influence the width or thickness of lines which are to be drawn by the exposed portion of the ball. The principle underlying the operation of the just described implements is the same as that underlying the operation of standard ball point pens, i.e., the delivery of ink onto the surface of a carrier is effected exclusively by the exposed portion of the ball and the rate of such delivery depends on a number of often unpredictable factors including the viscosity of the flowable medium, the ability of the ball to turn in the tip of the writing implement and others. The medium is or can be caused to flow toward the ball by capillary action; however, no capillary forces are involved in actual application of the medium to the surface of a carrier, such as a sheet of paper or a foil. If the front end face of the tip of a ball point pen or a like writing implement happens to contact the surface of the carrier, such contact is purely accidental.